This invention relates to an apparatus and method for enhancing the system response of a photodetector array based spectrometer.
The performance of a spectrometer is generally determined by the signal-to-noise (S/N) ratio of the system in the entire operating spectral range. Ideally, the spectrometer should provide a constant and high S/N ratio over the range. However, due to various technical limitations in prior art spectrometers, it has been very difficult or impossible to achieve a constant, high S/N ratio over a wide range mainly because of spectral variations in available light intensity and spectral variations of detector sensitivity. In scanning type spectrometers, this problem can be at least partially resolved with A suitable electronics design, exhibiting a response which may vary depending on signal level to secure the best S/N ratio at each measurement point. However, in photodetector array based instruments, where the complete spectrum is registered simultaneously applying constant electronic gain, the above approach cannot be used. Consequently, a new approach to providing a relatively constant and high S/N ratio across the entire operating spectral range is needed.
Accordingly, it is an object of the present invention to provide an apparatus and method of enhancing the system response of a photodetector based spectrometers which addresses some of the limitations of prior art instruments.
In one aspect, the present invention provides a method for improving the system response of a photodetector array based spectrometer having a main light source with a primary spectral component, comprising the steps of: (i) determining a system response curve for said spectrometer over said spectrometer""s operating spectral range; (ii) identifying at least one spectral band at which the system response curve falls below a predetermined value; and (iii) adding at least one secondary light source with a secondary spectral component complementary to said at least one spectral band identified in step (ii) so as to produce a combined spectral output which provides a modified system response curve which is at or above said predetermined value at said spectral band.
In an embodiment of the present invention, the method further comprises the step of filtering said combined spectral output so as to reduce peaks in the system response curve.
In another embodiment, the method may further comprise the step of masking said photodetector array so as to equalize the system response curve.
In another aspect, the present invention provides a light source for a photodetector array based spectrometer, said light source comprising a primary light source producing a primary spectral output which results in a characteristic system response curve, said light source further including at least one secondary light source producing a secondary spectral component which combines with said primary spectral output, whereby, said combined spectral output results in a more uniform system response curve that is flatter than the system response curve obtained when a primary light source alone is used.
In one embodiment, the secondary light source is a broadband light source having a shaping filter.
In another embodiment, the secondary light source is a narrow band light source.
In yet another embodiment, the narrow band light source is selected from the group consisting of a narrow band fluorescent light source, a light emitting diode, and a laser.
In a further embodiment, the multiple light sources are combined by means of multiple branches of fibre optic bundles.
Other features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the invention are given by way of illustration only. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.